Evolutionary Forces I - Key Terms (Skin Color, Selection, Drift, Phylogeny, Speciation, Physiology)

Vocabulary flashcards covering core terms from evolution, population genetics, speciation, phylogeny, and physiology.

UV radiation

Sunlight that varies in intensity by latitude; highest exposure at low latitudes.

eumelanin

Brown/black skin pigment that absorbs UV radiation and protects folate in the blood.

pheomelanin

Red/brown skin pigment contributing to lighter pigmentation; its amount varies among individuals.

folate

B vitamin important for embryonic development and sperm production; UV exposure can destroy folate.

selective pressure

Any factor that gives some phenotypes a survival or reproductive advantage or disadvantage.

polygenic trait

A trait determined by alleles of multiple genes; skin color is a classic polygenic trait.

allele

A variant form of a gene found at the same locus on a chromosome.

gene

A unit of heredity that resides on a chromosome and influences a trait.

skin color

Visible pigmentation of the skin influenced by multiple genes and environmental factors.

evolutionary forces

Processes that cause allele frequencies to change: mutation, natural selection, genetic drift, gene flow.

natural selection

Differential survival and reproduction leading to changes in allele frequencies over generations.

positive selection

Increase in frequency of beneficial variants that improve fitness.

negative selection

Removal of deleterious variants; does not favor harmful changes and can oppose certain evolutions.

directional selection

Selection that shifts the population mean toward one extreme.

stabilizing selection

Selection that favors average trait values and reduces variation.

disruptive selection

Selection that favors extreme traits over the mean, increasing variation.

frequency-dependent selection

Fitness of a phenotype depends on its frequency in the population.

positive frequency-dependent selection

Common phenotypes have higher fitness; rare phenotypes are selected against.

negative frequency-dependent selection

Rare phenotypes have higher fitness; common phenotypes are selected against.

genetic drift

Random changes in allele frequencies due to chance, especially in small populations.

bottleneck effect

Drastic reduction in population size leading to loss of genetic diversity and altered allele frequencies.

founder effect

Loss of genetic variation when a new population is established by a small number of individuals.

gene flow

Transfer of alleles between populations (migration); can hinder local adaptation.

habitat isolation

Prezygotic barrier where species occupy different habitats and rarely meet.

temporal isolation

Prezygotic barrier where species breed at different times.

behavioral isolation

Prezygotic barrier where courtship or mating signals are not recognized between species.

mechanical isolation

Prezygotic barrier due to incompatible reproductive structures.

gametic isolation

Prezygotic barrier where sperm and egg are incompatible or fail to fuse.

prezygotic barrier

Barriers that prevent fertilization before zygote formation.

postzygotic barrier

Barriers that reduce fitness of hybrids after fertilization.

hybrid inviability

Hybrid offspring fail to develop or survive to adulthood.

hybrid infertility

Hybrids are sterile and cannot produce offspring.

hybrid breakdown

F1 hybrids are viable, but later generations are inviable or infertile.

allopatric speciation

Speciation due to geographic isolation creating reproductive barriers.

vicariance

Geographic splitting of a population causing isolation and divergence.

dispersal

Movement of individuals to a new area, initiating geographic isolation.

sympatric speciation

Speciation without geographic isolation; divergence occurs in same area.

polyploidy

More than two complete chromosome sets; common in plants and can drive speciation.

autopolyploidy

Polyploidy arising from duplication within a single species.

allopolyploidy

Polyploidy arising from hybridization between two species.

ancestral trait

A trait present in the common ancestor of a group.

derived trait

A trait that is different from the ancestral state in descendants.

homologous trait

Shared traits inherited from a common ancestor, used to infer phylogeny.

analogous trait

Similar traits due to convergent evolution, not shared ancestry.

convergent evolution

Independent evolution of similar traits in different lineages due to similar pressures.

clade

A lineage and all its descendants; a monophyletic group.

monophyletic

A group consisting of a common ancestor and all its descendants.

taxon (taxa)

A named group in classification (e.g., vertebrates); may or may not be a clade.

phylogeny

The evolutionary history of relationships among organisms.

phylogenetic tree

A diagram showing evolutionary relationships based on shared traits.

lineage

A line of descent in a phylogenetic tree; a sequence of populations through time.

molecular clock

Hypothesis that molecular changes accumulate at a relatively constant rate to date divergences.

calibration

Using independent data (fossils, known dates) to align molecular clock estimates.

horizontal gene transfer

Movement of genes between organisms not via parent-offspring (lateral transfer).

endosymbiosis

One organism lives inside another and becomes a functional part of the host (mitochondria/chloroplasts originate this way).

gene duplication

Copying of a gene; copies may be nonfunctional, neofunctionalize, or subdivide functions.

pseudogene

A nonfunctional gene copy resulting from duplication and mutation.

de novo gene

New gene that arose from previously non-coding DNA.

transposable element

Mobile DNA that can move within the genome and create genetic variation.

surface area-to-volume ratio (SA/V)

Ratio governing exchange capacity; high in small/thin objects, low in large/thick ones.

homeostasis

Maintenance of a stable internal state in the face of environmental changes.

negative feedback

Regulatory feedback that opposes deviation from a set point.

positive feedback

Regulatory feedback that reinforces and accelerates a trend away from a set point.

countercurrent exchange

A system (often in gills or limbs) that maintains gradients to maximize exchange.

diffusion

Net movement of particles from high to low concentration down a gradient.

Fick’s law

Quantifies diffusion: Q = D A (P1 - P2) / L, where D is diffusion coefficient, A area, L path length.

ventilation

Active movement of air or water over gas exchange surfaces to increase P1.

perfusion

Blood flow over gas exchange surfaces to maintain P2 gradients.

respiratory media

Air or water used for gas exchange; differs in O2 content, density, viscosity.

oxygen dissociation curve

Relation between PO2 and Hb saturation; shifts with pH, temperature, CO2.

Bohr effect

Lower pH (more CO2) lowers Hb affinity for O2, promoting release in tissues.